1. Field of the Invention
This invention relates to a portable seismic system useful in exploration for subsurface minerals.
2. Description of the Prior Art
A good portable, reliable seismic source-detector system has long been needed in experimental and/or shallow high-resolution seismic data acquisition programs. The prior art mentions the use of weight drops, hammers, air guns, gas exploders, vibrators, small explosive charges, etc. However, each of these has disadvantages in one or more of the following areas: cost, service, coupling, portability, safety, reliability, energy or frequency content.
Pertinent prior art includes:
U.S. Pat. No. 3,509,820 to Fitch et al. teaches an explosive charge assembly that can be used in an underwater seismic operation. The charges are placed in large numbers in an offshore exploration area, and then fired when desired.
U.S. Pat. No. 3,878,790 to Meyer teaches an electronic shooting circuit for seismic operations. The circuitry delivers maximum current instantaneously to one or more electric blasting caps that are being detonated.
U.S. Pat. No. 2,544,573 to Vincent teaches an improved apparatus for well drilling containing one or more barrels through which projectiles are fired to fracture the formation. The sealed apparatus is lowered through the drill pipe to the bottom of the well and fired. The apparatus is withdrawn by way of an attached wire line.
Applicants have invented a portable, inexpensive system suitable for use in a wide variety of experimental, field testing, shallow check-shot survey and shallow, high resolution seismic data acquisition applications.
The explosive seismic source provided by this apparatus provides a broad band, highly directional explosive shock at an energy level comparable to a 24-inch base place Dinoseis truck. When fired at the bottom of a shallow hole (e.g. about 10 feet deep) most of the energy is directed downward and less ground roll, i.e. horizontal wave, is generated than from other comparable sources.